Noise levels generated during the installation of foundations for new offshore wind farms remain excessive, even when mitigation techniques are employed, according to the largest study of noise reduction options conducted thus far.
Final results of the ESRa noise mitigation project include the largest dataset yet detailing the effectiveness of new techniques to cut noise levels during piling.
While this information is valuable to those overseeing the environmental impacts of offshore wind projects during construction, results indicate that available mitigation techniques do not yet ensure compliance with the German government’s target for a 160 decibel limit at a distance of 750m from the noise source. Noise limits have been developed, in part, to protect the harbour porpoise.
Some of the techniques tested "brought the noise level much closer to the noise emission limit", although "more research and development work is required…to meet the limit reliably", according to the project conclusions.
Five techniques were tested last summer in the German Baltic Sea in a water depth of approximately 9m. The tests were supported by some of the biggest owner/operators active in Europe’s offshore wind industry, including Dong, Vattenfall, E.ON, EnBW, RWE, Stadtwerke Munchen, EWE and Bard.
The tests involved deployment of air-filled enveloping bodies, multi-layer hose curtains, bubble curtains, and a combination of acoustic cladding and bubble curtains.